This invention relates to hydraulic valves, and, more particularly, valves for use as margin valves in hydraulic systems.
Many hydraulic systems in use today employ flow and pressure compensated pumps and operate on a so-called "load plus" basis. In such systems, the pump is controlled to provide an output pressure that is equal to that required by the load plus some predetermined additional pressure increment commonly known as "margin".
In order to provide the margin, the systems have utilized so-called margin valves which typically had pump discharge pressure applied to one end of a spool and the load pressure plus a spring force applied to the other end of the spool for controlling a pilot signal to the pump control. In such systems, the spring force utilized was responsible for providing the margin.
In any event, such prior art margin valves had tended to be unstable in that load signals would cause the spool to overshift and, typically, would result in some period of oscillation of the spool. This, in turn, would result in a pilot signal of varying magnitude being applied to the pump control with the further consequence that the pump output pressure would vary in an oscillating manner, making it difficult to exercise fine control over the load.